This application requests support to continue our exploration of ?-peptide structure and biologic function. We build herein on the three most exciting and impacting discoveries of the first funding cycle: (1) that carefully designed ?-peptides effectively mimic ?-helices and function as protein interaction inhibitors, with properties that are easily improved by combinatorial methods;(2) that ?-peptides can be engineered to traverse the plasma membrane and retain biologic function in the cytosol, without the addition of a large "octa-arginine" tag, facilitating their application to intracellular targets;and (3) that certain ?-peptides self-assemble spontaneously into bundles that resemble proteins in many ways, paving the way for their use as catalysts. Thus, the Specific Aims of this application are to first (Aim 1) move away from "proof-of-principle" targets, and design ?-peptide ligands for two well-validated drug targets that could benefit from the unique combination of properties embodied by a ?-peptide: the GLP-1 receptor (GLP-1R), a target of the antidiabetes drug ByettaTM, and the ErbB2 receptor, a target of the mAb HerceptinTM. We also describe ?-peptides that either inhibit or activate CXCR4 and CCR5 chemokine receptors from within the plasma membrane. In Aim 2, we described experiments to systematically optimize and exploit cell-permeable ?-peptides as a first step toward broadening their applicability to cytosolic targets. The fact that ?-peptides are immune to proteolytic degradation makes them uniquely capable of reporting on the myriad pathways by which peptides achieve uptake and traffic within the cell once they do. Finally in Aim 3 we describe two approaches to ?-peptide bundles with function. In Aim 3.1, we describe ? -peptides containing fluorinated side chains in place of ?hLeu, designed to guide bundle assembly in a membrane. We view this goal as particularly exciting, as the design of protein interfaces that assemble selectively in a membrane represents a formidable and currently unmet challenge in molecular design. In Aim 3.2, we describe two complementary approaches to ?-peptide bundles that bind metal ions, the essential first step in the design of ?-peptide catalysts. We believe that the experiments in this application will expand the frontiers of protein design and define guidelines for the construction of ?-peptides and bundles with increasingly sophisticated biologic function. PUBLIC HEALTH RELEVANCE: Protein-protein interactions on the cell surface or in the cytosol are grossly underexploited in human medicine. ?-peptides possess unique advantages as inhibitors of these interactions. This proposal explores these advantages in the context of diseases as diverse as type 2 diabetes, cancer, and AIDS.